GABA content in the retina of pigmented and albino rats.

Reduction of the melanin precursor DOPA associated with albinism leads to spatiotemporal disturbances in retinal neurogenesis and thus seems to be responsible for numerous neuronal alterations found in albino retinae. To investigate whether these cellular alterations are reflected in retinal neurotransmitter concentrations we compared the levels of GABA and glutamate in the retina of adult pigmented Long Evans and albino Wistar rats using reversed phase-liquid chromatography (RP-HPLC). When normalized to retinal weight, GABA levels showed a statistically insignificant trend to be lower and glutamate values to be higher in albinos than in pigmented animals. The ratio of glutamate to GABA was significantly higher in albino than in pigmented retinae. As numerous studies have shown that the balance between GABA and glutamate plays a crucial role for establishing direction selectivity, these results are discussed in relation to direction selectivity and defects in the optokinetic system of albinos.

Identification of a tyrosinase (TYR) exon 4 deletion in albino ferrets (Mustela putorius furo).

Albinism is due to a lack of pigmentation in hair, skin and eye, and has been shown to occur in several animal species. Mutations of the tyrosinase (TYR) gene account for albinism in domestic cats, rabbits, cattle, mice and rats. In this study, we demonstrate that a TYR mutation accounts for albinism in the ferret (Mustela putorius furo). The coding sequence of the five exons of TYR was determined in genomic DNA from wild-type pigmented 'sable' coloured and albino ferrets. It was not possible to amplify TYR exon 4 in albino ferrets originating from different breeds. The deletion of exon 4 in albino ferrets was confirmed by Southern blot hybridization of genomic DNA from albino and pigmented ferrets. This is the first report of a deletion of a TYR exon in a non-human mammal.

GABA-immunoreactive starburst amacrine cells in pigmented and albino rats.

In this study we tested whether the critical anatomical substrate for retinal direction selectivity is altered in albino mammals. We used dual immunostaining for GABA and choline acetyltransferase and quantitatively analyzed the number of double-labelled starburst amacrine cells in wild-type and albino rats. In albino rats, the percentage of ON-amacrine cells with high GABA content was significantly lower than in pigmented animals. OFF-amacrines did not significantly differ between the two rat strains. Thus, the decreased GABA content in ON-amacrine cells could reflect an altered neuronal substrate for retinal direction selectivity. These results are discussed in relation to the optokinetic deficits described in albino mammals.